Downhole drilling apparatus and method for use of same

ABSTRACT

A downhole drilling apparatus for interconnection in a casing or liner string having a drill bit disposed thereon for enabling the drilling of intersecting wellbores without removal of the drill bit is disclosed. In a disclosed embodiment, the apparatus comprises a housing having a window. A whipstock is disposed within the housing. Between the window and the whipstock is a filler. The whipstock and the filler define a central bore providing a fluid path through the apparatus. A back pressure valve may be disposed within the central bore to prevent back flow of fluids through the apparatus. Once the total depth of an initial wellbore is reached, the casing or liner string, including the apparatus, may be cemented in place. Thereafter, an intersecting wellbore may be drilled by laterally deflecting a second drill bit with the whipstock through the window of the housing.

BACKGROUND OF THE INVENTION

[0001] This invention relates in general to drilling a wellbore and, inparticular, to drilling an intersecting wellbore through a drill stringincluding well casing or liner and a downhole drilling apparatusinterconnected therein.

[0002] Without limiting the scope of the invention, its background isdescribed in connection with drilling a wellbore for hydrocarbonproduction, as an example.

[0003] Heretofore, in this field, a typical drilling operation hasinvolved attaching a drill bit on the lower end of a drill string androtating the drill bit along with the drill string to create a wellborethrough which subsurface formation fluids may be produced. As the drillbit penetrates the various earth strata to form the wellbore, additionaljoints of drill pipe are coupled to the drill string. During drilling,drilling fluid is circulated through the drill string and the drill bitto force cuttings out of the wellbore to the surface, and to cool thedrill bit.

[0004] Periodically as the drilling of the wellbore progresses, thedrill bit and drill string are removed from the wellbore and tubularsteel casing is inserted into the wellbore to prevent the wall of thewellbore from caving in during subsequent drilling. Typically, aftercasing is inserted into the wellbore, the annulus between the casing andwellbore is filled with a cement slurry that hardens to support thecasing in the wellbore. Thereafter, deeper sections of wellbore withprogressively smaller diameters than the previously installed casing maybe drilled.

[0005] Once a predetermined depth is reached for each subsequent sectionof wellbore, the drill bit and drill string are again removed from thewellbore and that section of the wellbore may be cased. Alternatively,however, a liner may be used to case an open section of wellbore insteadof a full casing string. The liner, which is a string of connectedlengths of tubular steel pipe joints, is lowered through the casing andinto the open wellbore. At its upper end, the liner is attached to asetting tool and liner hanger. The liner hanger attaches the liner tothe previous casing such that the casing will support the weight of theliner.

[0006] The length of the liner is predetermined such that its lower endwill be proximate the bottom of the open wellbore, with its upper end,including the liner hanger, overlapping the lower end of the casingabove. As with the casing, after the liner is inserted into thewellbore, the annulus between the liner and the wellbore may be filledwith a cement slurry that hardens to support the liner in the wellbore.

[0007] It has been found, however, that in many well drilling operationsit is desirable to minimize rig time by utilizing the casing or linerstring as the drill string for rotating a drill bit, which may be leftin the wellbore upon the completion of drilling a section of thewellbore. As such, this procedure does not require the use of a separateliner or casing upon the withdrawal of the drill bit and drill string asin conventional drilling operations, and thereby reduces the time neededto drill, case and cement a section of wellbore.

[0008] For example, attempts have been made to utilize the casing orliner string as the drill string along with a drill bit that isrotatable relative to the casing or liner string. The drill bit isrotated by a downhole drill motor that is driven by drilling fluid. Uponcompletion of drilling operations, the motor and the retrievableportions of the drill bit may be removed from the wellbore so thatfurther wellbore operations, such as cementing, may be carried out andfurther wellbore extending or drilling operations may be conducted. Thissystem, however, requires the use of expensive and sometimes unreliabledownhole drill motors and a specially designed drill bit.

[0009] Alternatively, other attempts have been made to utilize thecasing or liner string as the drill string using conventional rotarytechniques wherein the drill bit is rotated by rotating the entirecasing or liner string. This approach, however, requires the use of adrill bit with minimal cutting structure, since a drill out could not beperformed through a typical drill bit having a full cutting structure,such as a tricone bit.

[0010] Therefore, a need has arisen for a drill string which may be usedas a well casing or liner, which includes a drill bit on its lower end,and which, upon completion of drilling operations, may be retainedwithin the wellbore without the need to retrieve the drill bit or thedrill string. A need has also arisen for such a well casing or linerstring that may be left in the wellbore along with a drill bit, andwhich does not require the use of expensive, unreliable or specialtyequipment. Further, a need has arisen for such a well casing or linerstring which may be cemented in place along with a drill bit having afull cutting structure.

SUMMARY OF THE INVENTION

[0011] The present invention, as exemplified by an embodiment disclosedherein, comprises a downhole drilling apparatus that is interconnectablein a casing or liner drill string and includes a drill bit connectedthereto which, upon completion of drilling operations, may be retainedwithin the wellbore without the need to retrieve the drill bit or thedrill string. The apparatus allows the well casing or liner to be leftin the wellbore along with the drill bit and does not require the use ofexpensive, unreliable or specialty equipment. The apparatus also allowsfor the well casing or liner to be cemented in place along with a drillbit having a full cutting structure.

[0012] The downhole drilling apparatus includes a housing that isinterconnectable in a casing string. The housing has a window cuttherein to allow a subsequent drill bit and pipe string to passtherethrough during a drill out operation. To facilitate the deflectionof the drill bit and pipe string through the window, a whipstock isdisposed within the housing. A filler material is also disposed withinthe housing between the whipstock and the window to prevent the flow ofdrilling fluids or cement through the window prior to the drill out. Thefiller and the whipstock have a central bore that permits the passage offluids through the center of the downhole drilling apparatus. One ormore valves may be disposed within the central bore to control the flowof fluids therethrough. The valves may be, for example, back pressure orfloat valves that allow one-way flow of fluids downwardly through theapparatus.

[0013] A drill bit having a full cutting structure, such as a triconebit, may be operably coupled to the downhole drilling apparatus. Thecasing or liner string may be used to rotate the drill bit.Alternatively, a downhole motor may be coupled between the downholedrilling apparatus and the drill bit to facilitate rotation of the drillbit, without the need for rotating the casing string.

[0014] In another embodiment, a downhole drilling apparatus includes ahousing having a window, an alignment member disposed within the housingand a back pressure valve assembly. The back pressure valve assemblyincludes a central bore that permits the passage of fluids therethrough.Once downhole, a whipstock may be run into the apparatus such that thewhipstock operably engages the alignment member. The alignment memberorients the whipstock within the housing relative to the window, so thatthe drill bit may subsequently be deflected through the window.

[0015] In operation, either embodiment of the downhole drillingapparatus may be interconnected in a casing or liner string having adrill bit disposed on its lower end. A first wellbore is drilled.Following the drilling of the first wellbore, the casing or liner stringmay be cemented within the wellbore. A pipe string having another drillbit on its lower end is passed through the casing or liner string, suchthat a drill out through the downhole drilling apparatus is performed todrill a second wellbore. The pipe string and drill bit that are used tocreate the second wellbore are deflected through the window in thehousing of the downhole drilling apparatus by the whipstock disposedwithin the apparatus.

[0016] Thus, with the use of the downhole drilling apparatus, a casingor liner string including a drill bit having a full cutting structuremay be used as a drill string to create a wellbore. The drill string maybe cemented in place within the wellbore, and thereafter have a drillout performed therethrough to create an intersecting wellbore.

[0017] These and other features, advantages, benefits and objects of thepresent invention will become apparent to one of ordinary skill in theart upon careful consideration of the detailed description ofrepresentative embodiments of the invention hereinbelow and theaccompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

[0018] For a more complete understanding of the present invention,including its features and advantages, reference is now made to thedetailed description of the invention, taken in conjunction with theaccompanying drawings of which:

[0019]FIG. 1 is a schematic illustration of an offshore oil and gasplatform during a drilling operating wherein a downhole drillingapparatus embodying principles of the present invention is utilized;

[0020]FIG. 2 is a schematic illustration of a first downhole drillingapparatus embodying principles of the present invention;

[0021]FIG. 3 is a cross sectional view of the downhole drillingapparatus of FIG. 2, taken along line 3-3;

[0022]FIG. 4 is a cross sectional view of the downhole drillingapparatus of FIG. 2, taken along line 4-4;

[0023]FIG. 5 is a schematic illustration of an offshore oil and gasplatform during a drilling operating wherein a downhole drillingapparatus embodying principles of the present invention is beingutilized in conjunction with a downhole motor;

[0024]FIG. 6 is a cross sectional view of a second downhole drillingapparatus embodying principles of the present invention before insertionof a whipstock therein; and

[0025]FIG. 7 is a cross sectional view of the second downhole drillingapparatus after insertion of a whipstock therein.

DETAILED DESCRIPTION

[0026] While the making and using of various embodiments of the presentinvention are discussed in detail below, it should be appreciated thatthe present invention provides many applicable inventive concepts whichcan be embodied in a wide variety of specific contexts. The specificembodiments discussed herein are merely illustrative of specific ways tomake and use the invention, and do not limit the scope of the invention.

[0027] Referring to FIG. 1, an offshore oil and gas platform isschematically illustrated and generally designated 10. Asemi-submersible platform 1 2 is centered over a subterranean oil andgas formation 14 located below sea floor 16. A well 18 extends throughthe sea 20, penetrating sea floor 16 to form wellbore 22, whichtraverses various earth strata. A wellbore extension is formed bywellbore 24, which extends from wellbore 2 2 through additional earthstrata, including formation 14.

[0028] Platform 12 has a hoisting apparatus 26 and a derrick 28 forraising and lowering pipe strings, such as drill string 30, includingdrill bit 3 2 located in wellbore 24, and casing string 34, includingdrill bit 36, crossover subassembly 38 and downhole drilling apparatus40 located in wellbore 22. As used herein, the term “casing string” isused to refer to a tubular string which includes sections of casing orliner.

[0029] As in a typical drilling operation, wellbore 22 is formed byrotating drill bit 36 while adding additional sections of pipe to casingstring 34. When drill bit 36 reaches total depth, however, casing string34 and drill bit 36 are not retrieved from wellbore 22. Rather, casingstring 34 and drill bit 36 are cemented in place by cement 42 whichfills the annular area between casing string 34 and wellbore 22.

[0030] Cementing casing string 34 and drill bit 36 in place withinwellbore 22 is a cost effective alternative to conventional drilling, inthat significant rig time is saved by minimizing the number of tripsinto and out of wellbore 22. At least one trip out of wellbore 22 andone trip into wellbore 22 are saved by using downhole drilling apparatus40. Additionally, the use of downhole drilling apparatus 40 avoids thepossibility of collapse of wellbore 22, particularly in unconsolidatedor weakly consolidated formations.

[0031] Alternatively, downhole drilling apparatus 40 may be used inconjunction with conventional drilling operations once a conventionaldrill string and bit have been tripped out of wellbore 22. For example,if wellbore 22 has traversed an unconsolidated or weakly consolidatedformation and it is likely that a collapse has occurred within wellbore22, it may be necessary to reopen that portion of wellbore 22. In thiscase, wellbore 22 may be reopened using casing string 34 with downholedrilling apparatus 40 and drill bit 3 6.

[0032] Once cementing of wellbore 22 has been completed, wellbore 24 maybe drilled. Drill bit 32 creates wellbore 24 by traveling through window44 of downhole drilling apparatus 40, as will be more fully discussedwith reference to FIGS. 2-4 below. As drill bit 32 and drill string 30continue to form wellbore 24, formation 14 is traversed. Note that thedrill string 30 may include another apparatus 40, if desired.

[0033] Even though FIG. 1 depicts wellbore 22 as a vertical wellbore, itshould be understood by those skilled in the art that wellbore 22 may bevertical, substantially vertical, inclined or even horizontal. It shouldalso be understood by those skilled in the art that wellbore 22 mayinclude multilateral completions wherein wellbore 22 may be the primarywellbore having one or more branch wellbore extending laterallytherefrom, or wellbore 22 may be a branch wellbore. Additionally, whileFIG. 1 depicts an offshore environment, it should be understood by oneskilled in the art that the use of downhole drilling apparatus 40 isequally well suited for operation in an onshore environment.

[0034] Schematically illustrated in FIG. 2 is a downhole drillingapparatus 50 embodying principles of the present invention. Apparatus 50has a pin end 52, so that the apparatus 50 is interconnectable in adrill string, such as casing string 34 of FIG. 1. Downhole drillingapparatus 50 also has a box end 54 that may be threadedly connected tocrossover subassembly 38 as depicted in FIG. 1.

[0035] Apparatus 50 has a generally tubular housing 56 with a window 58cut through a sidewall thereof. Window 58 is generally ellipticallyshaped and is sized such that a drill bit, such as drill bit 32 of FIG.1, may pass therethrough during a drill out operation.

[0036] Now referring to FIG. 3, a cross sectional view of downholedrilling apparatus 50 taken along line 3-3 of FIG. 2 is depicted.Disposed within housing 56 of apparatus 50 is a whipstock 60. A centralbore 62 extends through whipstock 60 to provide fluid passage fordrilling mud and cement through apparatus 50 during drilling andcementing operations. Valves 64, 66 are disposed within central bore 62of the downhole drilling apparatus 50. Valves 64, 66 may be backpressure or float valves that allow one-way flow of drilling mud orcement through the apparatus 50. As an example, valves 64, 66 may beSuperSeal II back pressure valves, available from Halliburton EnergyServices, Inc. of Duncan, Okla.

[0037] Whipstock 60 has an inclined upper surface, so that it directs adrill bit, such as drill bit 32 of FIG. 1, through window 58 of downholedrilling apparatus 50. Whipstock 60 may be constructed of any material,such as steel, having sufficient strength to deflect a drill bit throughwindow 58. Whipstock 60 may also provide additional torsional strengthto the downhole drilling apparatus 50.

[0038] A filler 68 occupies the volume between whipstock 60 and window58 of downhole drilling apparatus 50. Filler 68 prevents the flow ofdrilling mud or cement through window 58 of apparatus 50. Filler 68 maybe, for example, concrete that has been poured into downhole drillingapparatus 50. Window 58 may also be filled with filler 68 to provideprotection to window 58. Other suitable solid materials, such as resins,may be used for filler 68, so long as they set sufficiently and permitthe directional passage of a drill bit through window 58 of apparatus50.

[0039] In operation, when a drill bit, such as drill bit 32 of FIG. 1,encounters whipstock 60, the drill bit cuts through filler 68 and isdeflected laterally by whipstock 60 toward window 58 in housing 56.Window 58 is wider that the outer diameter of the drill bit, permittingthe drill bit to laterally exit the apparatus 50.

[0040] Referring now to FIG. 4, a cross sectional view of downholedrilling apparatus 50 is depicted that is taken along line 4-4 of FIG.2. Apparatus 50 includes housing 56, whipstock 60, filler 68 and window58. As with typical drill down shoes, downhole drilling apparatus 50 mayhave sufficient torsional strength to rotate a drill bit, such as drillbit 36 of FIG. 1. The wall thickness of housing 56 and the size ofwindow 58 will affect the torsional strength of downhole drillingapparatus 50. Of course, the window 58 should be dimensioned to permit adrill bit to pass therethrough.

[0041] The shape of whipstock 60 can be varied to maximize itsdeflecting capability. For example, whipstock 60 may be made concave orconvex to direct a drill bit, such as drill bit 32, through window 58 ofdownhole drilling apparatus 50. If whipstock 60 is made concave, drillbit 32 will encounter window 58 at a position slightly below that wherea straight whipstock 60 would direct the bit. Conversely, a convexwhipstock 60 will force the encounter of drill bit 32 with window 58 ata position above that of the flat-surfaced whipstock 60.

[0042] Referring now to FIG. 5, an offshore oil and gas platform isschematically illustrated and generally designated 70. Asemi-submersible platform 72 is centered over a subterranean oil and gasformation 74 located below sea floor 76. A well 78 extends through thesea 80, penetrating sea floor 76 to form wellbore 82, which traversesvarious earth strata. Wellbore 82 has a wellbore extension that isformed by wellbore 84, which extends from wellbore 82 through additionalearth strata, including formation 74.

[0043] Platform 72 has a hoisting apparatus 86 and a derrick 88 forraising and lowering pipe strings, such as drill string 90, includingdrill bit 9 2 located in wellbore 84, and casing string 94, includingdrill bit 96, downhole motor 98, crossover subassembly 100 and downholedrilling apparatus 102 located in wellbore 82. Using downhole motor 98,it is not necessary to rotate casing string 94, including downholedrilling apparatus 102, in order to rotate drill bit 96.

[0044] Drilling mud, used to cool drill bit 96 and carry cuttings to thesurface, also provides the power to operate downhole motor 98. As thedrilling mud travels through downhole motor 98, downhole motor 98imparts rotation to drill bit 96, so that wellbore 82 is drilled. Usingdownhole motor 98 in conjunction with downhole drilling apparatus 102reduces the torsional stress typically encountered by downhole drillingapparatus 102 when casing string 94 is used to rotate drill bit 96. Thisreduction in torsional stress allows for the use of a maximum widthwindow 106 in downhole drilling apparatus 102.

[0045] When drill bit 96 reaches total depth, casing string 94,including drill bit 96, downhole motor 98, crossover subassembly 100 anddownhole drilling apparatus 102, is not retrieved from wellbore 82.Rather, casing string 94 is cemented in place by cement 104, which fillsthe annular area between casing string 94 and wellbore 82.

[0046] Once cementing of wellbore 82 has been completed, wellbore 84 maybe drilled using downhole drilling apparatus 102. Drill bit 92 createswellbore 84 by traveling through window 106 of downhole drillingapparatus 102 in the manner discussed above with reference to FIGS. 2-4.

[0047] Referring next to FIG. 6, a cross sectional view of anotherdownhole drilling apparatus 120 embodying principles of the presentinvention is depicted. Downhole drilling apparatus 120 has a pin end122, so that downhole drilling apparatus 12 is interconnectable in adrill string, such as casing string 94 of FIG. 5, or to other downholetools. Downhole drilling apparatus 120 also has a box end 123 which maybe threadedly connected to crossover subassembly 100 as depicted in FIG.5.

[0048] Apparatus 120 has a generally tubular housing 124 with a window126 cut through a sidewall thereof. Window 126 is generally ellipticallyshaped and is sized such that a drill bit, such as drill bit 92 of FIG.5, may pass therethrough during a drill out operation. Surroundingwindow 126 is a cover or shield 128 that prevents the flow of drillingmud or cement through window 126. Apparatus 120 also has at least onealignment member 130, such as a track, within housing 124.

[0049] Disposed within housing 124 is a back pressure valve assembly132. A central bore 134 extends through back pressure valve assembly 132to provide fluid passage for drilling mud and cement used duringdrilling and cementing operations. Valves 136, 138 are disposed withincentral bore 134 of back pressure valve assembly 132. Valves 136, 138may be back pressure valves or float valves that allow one-way flow ofdrilling mud or cement therethrough.

[0050] As best seen in FIG. 7, a whipstock 140 may be run into downholedrilling apparatus 120 to direct a drill bit, such as drill bit 92 ofFIG. 5, through window 126 of apparatus 120. Whipstock 140 may beinstalled within downhole drilling apparatus 120 following a cementingoperation and subsequent use of a conventional cementing plug 142.Whipstock 140 includes one or more alignment lugs 144 that cooperatewith track 130 of downhole drilling apparatus 120 to radially orientwhipstock 140 with respect to window 126.

[0051] After cementing the casing string 94 within wellbore 82,including installing the plug 142 in the drilling apparatus 120, thewhipstock 140 is conveyed into the drilling apparatus. The alignmenttrack 130 and lugs 144 cooperatively engage and thereby radially orientthe whipstock 140 to face toward the window 126. A drill bit may then bedeflected off of the whipstock 140 to cut through the shield 128, or theshield may be previously displaced to open the window 126, for example,by using a conventional shifting tool.

[0052] In the embodiments described above, the present inventionprovides the ability to drill a wellbore using a well casing or linerstring as the drill string, and using a drill bit having a full cuttingstructure. The use of a downhole drilling apparatus embodying principlesof the present invention as part of the drill string allows a wellextension to be drilled from the existing wellbore, without having tobore through a drill bit on the end of the casing or liner string. Thus,trips into and out of the wellbore may be eliminated and a drill bithaving a full cutting structure may be used.

[0053] While this invention has been described with reference toillustrative embodiments, this description is not intended to beconstrued in a limiting sense. Various modifications and combinations ofthe illustrative embodiments, as well as other embodiments of theinvention, will be apparent to persons skilled in the art upon referenceto the description. It is, therefore, intended that the appended claimsencompass any such modifications or embodiments.

What is claimed is:
 1. A downhole drilling apparatus comprising: agenerally tubular housing having a window formed through a sidewallthereof; a whipstock disposed within the housing; a filler disposedwithin the housing between the window and the whipstock; and a boreextending through the housing and permitting passage of fluidstherethrough.
 2. The apparatus according to claim 1, further comprisinga drill bit operably coupled to the housing.
 3. The apparatus accordingto claim 2, further comprising a downhole motor operably coupled betweenthe housing and the drill bit.
 4. The apparatus according to claim 1,wherein the filler further comprises concrete.
 5. The apparatusaccording to claim 1, wherein the filler further comprises a resin. 6.The apparatus according to claim 1, further comprising a back pressurevalve for controlling flow of fluids through the bore.
 7. The apparatusaccording to claim 6, wherein the valve allows one-way flow of fluidstherethrough.
 8. The apparatus according to claim 1, further comprisingfirst and second valves for controlling flow of fluids through the bore.9. The apparatus according to claim 1, wherein the window in the housingis elliptical.
 10. The apparatus according to claim 1, wherein the boreis formed through the whipstock.
 11. The apparatus according to claim 1,wherein the bore is formed through the filler.
 12. A downhole drillingapparatus comprising: a generally tubular housing having a window formedthrough a sidewall thereof; a whipstock disposed within the housing; afiller disposed within the housing between the whipstock and the window;a bore extending through the housing and permitting passage of fluidstherethrough; and a back pressure valve for controlling fluid flowthrough the bore.
 13. The apparatus according to claim 12, furthercomprising a drill bit operably coupled to the housing.
 14. Theapparatus according to claim 13, further comprising a downhole motoroperably coupled between the housing and the drill bit.
 15. Theapparatus according to claim 12, wherein the filler further comprisesconcrete.
 16. The apparatus according to claim 12, wherein the fillerfurther comprises a resin.
 17. The apparatus according to claim 12,wherein the valve allows one-way flow of fluids therethrough.
 18. Theapparatus according to claim 12, wherein the window in the housing iselliptical.
 19. The apparatus according to claim 12, wherein the bore isformed through the whipstock.
 20. The apparatus according to claim 12,wherein the bore is formed through the filler.
 21. A downhole drillingapparatus comprising: a generally tubular housing having a window formedthrough a sidewall thereof; an alignment member disposed within thehousing; and a back pressure valve assembly operably associated with thehousing, the back pressure valve assembly having a bore that permits thepassage of fluids therethrough.
 22. The apparatus according to claim 21,further comprising a whipstock operably engaged with the alignmentmember, thereby orienting the whipstock within the housing relative tothe window.
 23. The apparatus according to claim 21, further comprisinga shield preventing flow of fluids through the window.
 24. The apparatusaccording to claim 21, further comprising a drill bit operably coupledto the housing.
 25. The apparatus according to claim 21, furthercomprising a downhole motor operably coupled between the housing and thedrill bit.
 26. The apparatus according to claim 21, wherein the backpressure valve assembly allows one-way flow of fluids therethrough. 27.The apparatus according to claim 21, further comprising first and secondvalves for controlling flow of fluids through the bore.
 28. Theapparatus according to claim 21, further comprising a cementing plugpositioned between the back pressure valve assembly and a whipstock. 29.The apparatus according to claim 21, wherein the window in the housingis elliptical.
 30. A method of drilling intersecting first and secondwellbores, the method comprising the steps of: coupling a downholedrilling apparatus within a first pipe string, the first pipe stringhaving a first drill bit disposed on a lower end thereof; drilling thefirst wellbore; disposing a second drill bit on a lower end of a secondpipe string; running the second drill bit into the first pipe string;and drilling laterally through the downhole drilling apparatus to drillthe second wellbore.
 31. The method according to claim 30, furthercomprising the step of cementing the first pipe string within the firstwellbore.
 32. The method according to claim 30, further comprising thestep of disposing a downhole motor between the downhole drillingapparatus and the first drill bit.
 33. The method according to claim 30,wherein in the coupling step the downhole drilling apparatus includes ahousing having a window, a whipstock disposed within the housing, afiller disposed within the housing between the window and the whipstock,and a bore extending through the housing and permitting passage offluids therethrough.
 34. The method according to claim 33, wherein thestep of drilling through the downhole drilling apparatus furtherincludes drilling through the window in the housing of the downholedrilling apparatus.
 35. The method according to claim 33, wherein thestep of drilling through the downhole drilling apparatus furtherincludes deflecting the second drill bit through the window with thewhipstock.
 36. The method according to claim 30, wherein in the couplingstep the downhole drilling apparatus includes a housing having a window,an alignment member disposed within the housing, and a back pressurevalve assembly operably associated with the housing, the back pressurevalve assembly having a central bore that permits the passage of fluidstherethrough.
 37. The method according to claim 36, further comprisingthe step of running a whipstock through the first pipe string andoperably engaging the whipstock with the alignment member to orient thewhipstock within the housing relative to the window.
 38. A method ofdrilling intersecting first and second wellbores, the method comprisingthe steps of: drilling at least a portion of the first wellboreutilizing a casing string which includes a generally tubular housingpositioned above a first drill bit, the housing having a window formedthrough a sidewall thereof; cementing the casing string in the firstwellbore; and drilling at least a portion of the second wellbore bydeflecting a second drill bit from within the casing string laterallyoutward through the housing window.
 39. The method according to claim38, wherein the cementing step is performed after the first wellboredrilling step and without removing the casing string from the firstwellbore.
 40. The method according to claim 38, wherein in the firstwellbore drilling step, a whipstock is positioned within the housing.41. The method according to claim 40, wherein in the first wellboredrilling step, a filler is disposed between the whipstock and thewindow.
 42. The method according to claim 40, wherein the first wellboredrilling step further comprises flowing drilling fluid through thewhipstock.
 43. The method according to claim 40, wherein the cementingstep further comprises flowing cement through the whipstock.
 44. Themethod according to claim 38, wherein in the first wellbore drillingstep, a downhole motor is interconnected between the housing and thefirst drill bit.
 45. The method according to claim 38, wherein in thefirst wellbore drilling step, a shield prevents fluid flow through thehousing window.
 46. The method according to claim 38, further comprisingthe step of conveying a whipstock into the housing after the cementingstep.
 47. The method according to claim 46, further comprising the stepof aligning the whipstock with the window by engaging the whipstock withan alignment structure of the housing.
 48. The method according to claim38, wherein in the first wellbore drilling step, a valve is disposedwithin the housing to control fluid flow therethrough.
 49. The methodaccording to claim 48, wherein in the first wellbore drilling step, thevalve permits fluid flow through the housing in only one direction. 50.The method according to claim 48, wherein in the first wellbore drillingstep, the valve is a back pressure valve.